Hysteresis
by arcanista
Summary: Sans investigates the abandoned ruins, looking for some sort of insight into the kid who's shambled into his life. The fallen child turns the screws. [Follow-up to Nobody Home.]
1. Hysteresis

_**Hysteresis**_ _is the time-based dependence of a system's output on present and past inputs. The dependence arises because the history affects the value of an internal state. To predict its future outputs, either its internal state or its history must be known._

* * *

 _what we've got here is a failure to communicate_

* * *

It's like living with a corroded bomb. It's going to go off, eventually, but there's no way to tell when exactly the faulty connections are going to fire. The tension feels like ants crawling up his spinal column.

But he can get used to anything, really. Sans figures the kid's finally worked out jokes. Not puns, not so much- if the kid's listening at all when he makes those, they just spend the whole time sounding out the words, far as he can tell. But the one about the elephant hiding in a strawberry patch got something like a smile out of the kid. Nothing like a good non sequitur.

Feels almost normal. That worries him some. Kind of like the time when he realized he'd gotten used to the looming threat of time unwinding, undoing everything back to its anchor, only now with the bonus threat of the kid going on a killing spree. Again. (He doesn't think, much, about the likely first victim of that; it makes his metacarpals itch. It would not be a good time, for anyone.)

Well, probably that risk had always been there. But how could he even tell?

It'd help if he knew anything he knew how to use. Or how to _get_ that information. The kid's of limited help- might be they could be more useful _if_ he knew what to ask. And they're not stable enough for him to be particularly satisfied with just letting it go, for both the kid's sake and everyone else's.

So he's got a black box to deal with. A really fragile black box with 'contents under pressure' written on the side that also rattles ominously on a regular basis. And it's not even his birthday.

He's got a pretty good eyewitness account of most of what happened after the kid left the ruins, to wit, his own. But as far as he can tell, ever since the kid left, time's been going on a straight-line path.

He shortcuts his way to the ruins. Seems as good a place as any to look for what he can find.

Sans' footsteps don't echo in the empty house, not with his good rubber-soled sneakers, not on the soft, dusty carpeting. Ordinary dust, from air and neglect. It's cozy and distantly familiar. He tries not to touch anything as he looks around, leaning back to see the top layer of the bookshelf.

In the kitchen, there are child-sized footprints in the dust, old enough that they're starting to dust over, too. They lead up to the counter, standing in front of a pie. Only one slice is missing, and the crust has gone rock-solid, but the rest looks fine. Sans dabs his pinky into the filling and tastes it. Butterscotch, and a bit of cinnamon, and a lot of dust. He shoves his hands in the pockets and leaves the kitchen.

He trudges past the living room and into the other hall. Some impulse leads him to skip the first door and go for the second. The shut door's kept the worst of the dust away, making this bedroom look nearly still lived in. A bucket of snails by the desk, a queen-sized bed. Casual interest as a collector induces him to look into the sock drawer. He picks out one, hand-knitted and striped, and pockets it.

Sans steels himself before looking at the open book on the desk. When he realizes it's a diary, he feels a bit awkward, but he settles his attention on a date marked by a circle.

"Heh..." he says, turning away. "Heh... yeah. Bonely. That was a good one. Sorry, lady. Your majesty, I guess. For what it's worth I think the kid is, too. I guess that's not worth much after all. Sorry. Hope it goes better for you next time."

But he stops before leaving the room and walks back to the desk. He picks up a pencil and flips the pages ahead, looking for today's date. Once there, he skritches, in loose, sloppy lettering:

 _What kind of art do skeletons like? Skullpture._

And he shuts the diary.

He turns and leaves, only now going into the first bedroom. Most of what's here is old, old enough for Sans to rule it out entirely as being meaningful: shoes and toys that look like they haven't been played with in years. But the bed's been slept in. Made, but slept in. Sans knows a good rumple when he sees one.

The pillowcase is salt-stained all over and has some faded rust-brown speckles all over it. When he picks up the pillow, he can see faint little scratches in the headboard's finish. Looks like fingernails, scrabbling for purchase, by his best guess. And here, a knotted tuft of hair in the crevice between mattress and headboard.

So. When the kid came out of here, they had already slaughtered everyone in the ruins and was ready to start on the forest. But the pie _had_ gotten through to the kid somehow, he knew that already. And in here, signs of a struggle. Probably a quiet one.

Then Sans thinks back to some of the only good info he's managed to get his hands on lately, and he thinks: _three times_. He shudders.

Doesn't give him the whys, but he feels okay penciling this in as a definite emergence of the kid's current state, prior to Papyrus. Makes it a bit less likely that the kid's faking, he figures. Not that he had that one very far on the table in the first place, but he's not in much of a position to be ruling things out.

There's probably more to investigate down here, so Sans starts walking. Less likely to be fruitful, all told, but he's already gone out of his way to be here, so better check it out now rather than have to come all the way back.

One last thing he wants to check, anyway. There's still the starting point, way in back.

* * *

Takes a careful look. Frowns as red and black blotches swim but catches a glimpse of a number through the haze. Lifts other hand and holds up four fingers.

"Fours?" Voice loud, but doesn't hurt. Warm and no edges. Easier to think around it. "Nyeh heh heh. There are no fours in my hand, human! Instead, you must _go fish_!"

Reaches out until cards underneath fingers. Picks out one, lifts it and slides it with the rest. Lowers head, peeks a little and finds number. Six. Wait. Yes. Two of them. Pulls first one out, then second. Places them on table. Smiles, looks up, uses eyes all the way for a second. Looks happy.

 _Good_ at numbers.

No, _I'm_ good at numbers. You can barely count to three. Should I make you try?

Fingers shake just a bit. Tries to ignore it, tries to listen outside instead. Misses the first part. "... have any nines!"

Examines cards one at a time. Squints, but numbers swim, can't read. Shuts eyes, opens them, tries again. Still can't. Laughing inside, somewhere. Keeps mouth shut.

"You can do it, human! Find your nines and give them to me!"

Fingers move without wanting it. Picks card and holds it out. Feels same smile as before. Wants to be sick everywhere.

What would you ever do without me?

Easier to relax, to let it happen. So easy. Looks at edge of table. Could hit head? Make it stop, maybe?

Not sure where that comes from. Head still hurts from fight. Takes big breath. Shivers. Doesn't do it. Won't.

Looks at cards again. Can read them now. Just imagining earlier? Puts cards down to hold up seven fingers. Feels them shake.

"I do have a seven!" Turns over hand for card. Fingerbones careful, places card so it doesn't drop. "You know, human, I'm very impressed with your progress through my signature being-a-better-person program (patent pending)."

You're slipping away by inches. Fingers close around card, easily. You'll let go. Puts card on table.

"Just think! It wasn't all that long ago when you were still being held back by your cultural aversion to puzzles!"

Lip quivers. Then when you do, I think we'll stay here for a while. Lifts cards, all one motion. You've made such good friends here.

"And look at us now! Playing cards together!"

Pulls out matching seven. I'm going to kill them. Rubs two cards against each other. Not just once. Smoothly puts them down.

"You've come so far... one day soon, I might even be able to tell Undyne I've found a human! And then you can be friends!"

I'm going to kill them, and then I'm going to reset things. Squeezes eyes shut tight. I'm going to kill them, over, and over, and over again.

"But I can tell you're not ready to meet her yet. So that's why I've prepared some ultra-special P̶̷̸̲̲̿a̶̷̸̲̲̿p̶̷̸̲̲̿y̶̷̸̲̲̿r̶̷̸̲̲̿u̶̷̸̲̲̿s̶̷̸̲̲̿ life advice for you (also patent pending)!"

Doesn't want to cry right now. I'm going to kill them, and they're going to scream, and you're going to scream with them. Trying so hard not to cry, squeezing eyes shut.

"Whenever life gets you down, you should always start by asking yourself: What would P̶̷̸̲̲̿a̶̷̸̲̲̿p̶̷̸̲̲̿y̶̷̸̲̲̿r̶̷̸̲̲̿u̶̷̸̲̲̿s̶̷̸̲̲̿ do in this situation? And you should do whatever it is I would do! And that will help you down the path of becoming a really cool person!"

I'm going to keep killing them until you're done screaming, until you're done crying, until every pathetic little scrap of you that's left is just curled up in a ball like the worthless trash that you are. Feels tears start to escape. Sniffles.

"Uh... human? That's not what I would do. But you can figure it out. Just keep trying!"

I'm going to kill them until there isn't enough left of you to resist. Stands up. Wobbles on feet. Hands on table, holds steady.

"Yes! Good choice! Standing up is one of the most important parts of the P̶̷̸̲̲̿a̶̷̸̲̲̿p̶̷̸̲̲̿y̶̷̸̲̲̿r̶̷̸̲̲̿u̶̷̸̲̲̿s̶̷̸̲̲̿ method! I stand up all the time!"

Tries to ignore it. Walks around table. Sniffles one more time. Wipes nose. Opens arms. Moves them wide and- hugs, warm. Not safe. But warm. Bony arms come around, tight but not too tight.

"One of the most powerful moves in my repertoire! You're getting there! If you face a truly unsurmountable problem, you should begin by offering a hug! I believe in you, human!"

Oh, and when I'm bored with it, I should give you a present. That's what friends are for, right? I should thank you for helping me have such a great time. I've got just the thing: _I'll give you their names._

Holds on tight until the crying stops. Stays determined.

* * *

It's nearly a beautiful little spot. Golden flowers grow wild in a neat rectangle, thriving somehow despite being unmaintained. The last time he was here, the flowers were dying. The last time was here, a child had spilled a queen's dust on them, and struggled for something meaningful to say. The last time he was here, he'd turned away and said under his breath the only words he could think of, for a friend he'd never seen.

Sans can't find this place beautiful. Not now. He can think of a hundred and one places he'd rather be, and some of them involve dress codes. But right now, this is where he needs to be.

He walks a circle around the flower patch, looking straight up. After about fifteen, twenty feet, the cavern walls start narrowing, but he can't see where, or if, they converge. Sans pulls his phone out of his pocket and takes a second to activate the flashlight. He holds the back of the phone up high, craning his neck to try and see how high up it goes.

The hole narrows more the higher it goes, but the light eventually vanishes in the gloom before it hits the top. He ticks the light off and puts the phone back in his pocket, rocking back and forth on his heels as he thinks. No matter what, it's a long, long way up. An even longer way down.

Probably worth seeing if any daylight at all can get in. Sans pulls his phone back out, and starts flipping through his apps. He finds one he can use easily enough, with only a couple tweaks.

He puts a pin in that thought long enough to text: _hey pap could be late tonight. found a great place to nap. should be back before storytime but dont sweat it if im late_

Then, as an afterthought, he logs into one of his parachute accounts on UnderNet. He sends: _coolskeleton95 great spaghetti recipes_ _click here!_ and schedules it to go out in two hours. Sans chuckles under his breath, and only then starts setting up for work.

Simple enough: use the camera's light sensor and have an alarm go off if it goes above a certain amount, or a certain amount of time has passed, twelve hours in this case. He finds a spot in the flower patch as close to the centre of the hole in the ceiling as he can estimate, and carefully bends the flowers aside around the phone, making sure the camera lens is unobscured.

Then he sits down against the cavern wall, and settles in to waiting. Sans rummages through his pockets until he comes up with a packet of ketchup, which he splits open and squeezes out into his mouth. The empty foil, he shoves in his pocket.

He pulls out an oversize deck of cards afterward, and starts shuffling, steady and thoroughly. Not a consistent or reliable testing device, but he'd might as well see what he can see.

The trick to anything at all dealing with ripples across timelines is that it's wildly susceptible to interference. Magic, blind luck, anything at all, really. Collecting information about either future or past potentialities is like sieving glitter from sand. Whole sciences had to be invented to figure out how to do that task.

Sans cuts the cards twice, then stacks them. Right now, in his hands, he's got one of the crudest methods- effectively, using a fork instead of a sieve. But maybe if he's lucky, doing this here in this place will give him something good. He sweeps some dust from the ground in front of him, and starts placing cards. One card for the kid in the centre, then one on top. One sideways across. Below, above, side to side. Four on the right, all in a vertical line. He sets the deck just to the side, just in case.

He starts flipping cards, interpreting as he goes: for the kid, oppression, obstacles. The heart of the situation, he gets deception, fear, mistakes. In opposition, he sees hope. Well, that's a good sign, anyway.

At the roots, a woman- older, cruel-intentioned. Sans reaches for the deck and pulls another card, tossing it atop her, hoping for a little more insight, maybe. He gets violence. Fatalism.

Sans cracks his knucklebones as he goes for the next, the card above, the one that calls directly for potentialities. Stasis. He flips the next two in rapid succession: the recent past is just ruin, the immediate future speaks to interference, obstructions.

One more card for the kid, for their own take on the situation, and it makes him laugh when he sees the card. A figure bound and hanging from a tree, signifying delay.

With crude lines done in blue marker, a hoodie's been sketched onto the figure. "Oh, kiddo," he says, and sighs.

But he smiles when he turns over the next, the one for the general environment: one cup, overflowing with water. He taps his index finger on it a couple times. "Think that one's you, Pap. That one's all you. You're good for the kid."

Hopes and fears are next, second last, and he draws isolation. That leaves only the ultimate outcome, and he groans when he sees the extent to which temporal mechanics have gone out of their way to prank him. Perseverance, he'd call this one normally. In this case?

Of course it's _determination_.

But taken as a whole, it's given him nothing he hasn't already guessed at: a scared kid who'd come out of a bad, bad situation, holding on by a thread. Improvement's there, but hard to reach. He's just about to sweep the cards away when he looks down and squints real hard at a particular combination.

Stasis. Delay. Perseverance.

"Kid's definitely stealing my move _,"_ Sans exhales into the cavern air. He's not sure if he's awed or disgusted by it. Not surprised, so much- he'd pretty much called it already, but he had less on the kid when he'd first guessed it. Not that he's got a lot now, but he's been making progress.

So the kid's fighting- something. Something they don't think they can win against.

Other than that, the cards aren't giving him much, unless he's made a critical mistake in the interpretation or in the question at hand. Both of which are very real possibilities at the best of times, which the present juncture clearly is not.

Still looking down at the cards, Sans runs things through his head. The kid sleeping on his and Papyrus' couch is _probably_ not the thing that slaughtered Snowdin Forest and these ruins. But the same being, somehow. That's a line of thought that only creates more questions than answers.

Sans tsks and wipes the spread, stacking the cards once more and doing a loose shuffle before shoving the deck away in his pocket. Killed some time, anyway. He pulls a magazine out of his hoodie and starts flipping through it.

By the time he's read the whole thing through three times, including the ads, he hears an insistent beep coming from his phone. Sans pushes to his feet, and goes to turn over the phone, looking at the numbers on the display. He takes a screenshot then looks up again.

He can tell the difference, barely. Whatever this faint grey haze is, it can't be what the history books meant when they talk about sunlight. But it's the closest he's going to get, and it's what he needs. No lights on his end, that'll just obscure things.

The sun at zenith over the hole to the underground is a tiny grey pinprick, high in the distance. Almost looks like a speck of dust. He might do the math later, but the actual numbers won't be too important, he doesn't think. It's a long, long, long fall.

Sans steps off the flower patch and turns back to straighten the flowers he'd bent out of the way. So, the opening on the other side can't be that big, or they'd have been swimming in humans this whole time. Couple options for how the kid could get down here, then.

First, a pure accident. Hard to say how likely that one is without knowing what the hole's like topside. But plausible, very plausible.

Second, it could have been intentional. Few ways that could go. Option one goes back to being a subset of the accident theory: under-estimating the depth of the drop. Possible, but his gut tells him that's not it. Option two: the kid anchored near the bottom and reset so they were dropping from a safe height.

Problems with option two: first, it's kind of convoluted. Second, does momentum get preserved when the kid anchors? Sans hasn't got a clue, and if the answer is yes, that would rule this one out entirely. Third: just what would it _mean_ for the kid to know about resetting before even falling down? Fourth: Why would the kid want to end up down here? And so on.

And then there's option three: the kid has a death wish. They fell intentionally, and survived, somehow.

So he has no good explanations for how the kid ended up down here. No leads as to how this started. At best, he's coming away with some more hope that there really is an honestly good kid deep down inside them. And that's not nothing, mind. It's a whole lot of something. But it's kind of a dead end as far as avenues to pursue go.

Well, he's got some math to do, and maybe sleeping on things will give him a better angle. He checks the clock on his phone and winces; definitely past Papyrus' story-time. Better get going- wait. Something moving close to the ground, in his peripheral vision. Sans turns and strolls back to the flower patch. All pretty golden flowers, staying in a neat spot, but growing wild, covering over the whole rectangle of soil. But there's a subtle little empty patch of dirt visible through the flowers a few inches in from the edge. When he takes a closer look, some of the nearby stems are bent, and one is outright severed.

And that tiny little exposed patch of dirt looks very much like a hole, collapsed in on itself, with a tiny sprinkle of golden pollen dusted on top.

"Damn it," says Sans. But nothing to be done for it now. Just needs to be more careful in the future.

He takes his shortcut home.

* * *

Sans makes a couple extra stops along the way, just to make sure he shakes the weed on his tailbone. Assuming it's still following him, and that's not a safe bet. But he needed to pick up chips anyway. Chips, and a book of crossword puzzles (maybe he can hide it from Papyrus long enough to get through at least a whole one, before all the answers get helpfully filled in with Zs), a book of Jumbles (some junior, some not), and a colouring book (with word searches!), and a pack of crayons (and okay, he might have secretly swapped the boring colours like 'burnt sienna' for more interesting ones instead).

He gets inside and kicks his shoes off into the closet, making sure they land further back than the kid's shoes, and steps into his slippers. The living room lights are all out- kid probably curled up in a corner, he figures- so he pockets his own book, tosses the colouring book and crayons onto the table, then goes to toss the chips into his half of the fridge.

There's noise coming from Papyrus' room that he can hear straight down from the bottom of the stairs. The door is ajar, so Sans knocks once before shuffling in.

"It goes 'Hruuugh!' It is a hippopotamus! That's not my cow!" Papyrus is sitting on the edge of the bed, a book open on his lap, one finger moving under a line of text. The kid's sitting next to him, head pointed intently in the direction of the book. Gotta hand it to him, Papyrus really makes a fantastic hippopotamus noise. But Papyrus stops as soon as he notices Sans come in.

"Hey Pap, kid," says Sans. "Sorry I'm late. You got the story in hand, or should I take over?" It's a tried-and-true method of avoiding uncomfortable questions: just change the subject _immediately_.

"What do you think, human?" says Papyrus, looking down at the kid. They rub their eyes blearily, but don't respond more than that uncommonly normal gesture. Papyrus soldiers on. "Well, you should do something to make up for sleeping all day! Here!" He thrusts the book out at Sans.

Sans just shakes his head and takes the book. "Scooch over, kid," he says, and takes a seat between them and Papyrus. "Start over at the beginning, I guess?"

And so with Papyrus looking over his shoulder and the kid under his arm, Sans tells the story of the missing cow. From sheep, to horse, to hippopotamus, and so on, he details the painstaking search of this one person for a missing cow, complete with all the barnyard noises Sans can muster. Impressions aren't really his strong suit, but that's not the point at all. Papyrus stays in suspense, and the kid tracks the movement of his fingerbone below the words.

Finally, he gets to the dramatic climax of the story. "Is that my cow? It goes 'Mooooo!'" Even the kid's into it, Sans thinks, mouth in an approximation of an o-shape. "Yes! That's my cow! Hooray, hooray, it's a wonderful day, for I have found my cow!"

Sans shuts the book then returns it to Papyrus' shelf, while the kid slowly pushes off the racecar bed. They wobble a bit as they stand, but steady out once they're upright. Sans stifles a yawn. "Well, I guess it's bedtime for everyone, then. You're having your nap now too, Papyrus?"

"I can't believe you're going back to sleep," says Papyrus. "I thought you were out napping all day! Instead of working!"

Sans picks up the kid with a little 'oof', and says, "Napping's hard work, okay. You could say it leaves me... bone tired." Papyrus groans loudly. "But thanks for keeping an eye on the kid today. I know your schedule's tight."

"No, the human's getting a lot better at being friendly!" says Papyrus. "Aren't you, human? We played cards and watched TV and had an important bonding moment!"

"Yeah? That so?" Sans looks to the kid, now that they're more at eye level. "You and my brother have a good time today, kiddo?"

A long pause, but that's nothing new from the kid. After a few moments, they nod a couple times, the motion ruined by a yawn coming out in the middle.

"Yeah, he's a lot of fun," says Sans. "But I think that's my cue to go put them to bed. I'll go to work tomorrow, okay?"

"You better," says Papyrus. "You still haven't recalibrated your puzzles!"

Sans carries the kid toward the door. "Yeah, I'll get on it. Night, Pap."

Papyrus shuts the door behind him. Sans carries the kid to the living room, bypassing the stairs. He puts them down on the couch, pulling up the good cushion and down behind the couch for the blanket. The kid'd just end up on the floor otherwise, and that just wouldn't be right.

"Hey, kid..." says Sans, tucking the kid in under the blankets. The kid looks up at him, blinking sleepily. Sans sighs. "... nah. Wish I knew what to ask you. You're kinda frustrating, kiddo."

They hang their head at that, and Sans regrets it. He moves to ruffle the kid's hair and stops short when he remembers how hair-shy the kid is. Instead he just lifts the kid's chin. "Don't worry about it. Hey, why'd the elephant stand on top of a marshmallow?"

The kid cocks their head, looking blank-eyed up at him. Sans delivers the punchline: "So she wouldn't fall into the hot chocolate." The kid makes a sound something like a hiccup. He thinks it's a giggle.

"There you go," says Sans. "Get a smile out of you yet." He hesitates, then adds, "Look, kid. You're doing good. Can you remember that for me?"

Now, that elicits a reaction. The kid's expression starts rearranging itself into one of seriously intense concentration: something like a jeweler engraving into titanium. They hold that look for two full minutes, then nod, right before their face blanks again. Interesting.

Sans stands up. He arranges the blankets a little more cozily around the kid. "Sleep tight, kiddo," he says, and heads upstairs.


	2. Supplemental Material

**The One About the Strawberry Patch**

 **Q:** How do elephants hide in strawberry patches?

 **A:** They paint their toenails red.

* * *

 **Sans' Cards**

Significator: 10 of Wands

Cover: The Moon

Cross: The Star

Ground: The Queen of Swords (Reversed) + The Devil

Crown: Death (Reversed)

Recent Past: The Tower

Near Future: 8 of Swords

Self: The Hanged Man

Environment: Ace of Cups

Hopes and Fears: The Hermit (Reversed)

Outcome: Nine of Wands

* * *

"Where's my Cow" excerpted from Thud! by Terry Pratchett. May he ride eternal, shiny and chrome.


End file.
